1. Field of the Invention
The present invention relates to a probe scanning device such as a scanning probe microscope, and particularly relates to a probe scanning device capable of measurement with little temperature drift and low noise.
2. Description of the Related Art
The applicant has previously invented a probe scanning device having a zooming function shown in FIG. 10 and applied for a patent (Japanese Patent Publication No. Hei. 10-221348). The structure and function of this probe scanning device will be briefly described below.
A case 1 has a scanning tube 20 having a thin tube 14 projecting to a sample chamber and a thick tube 15 connected thereto as main components. An inner tube 13 is supported inside the thick tube 15 through the viscous material 17. The thick tube 15, the inner tube 13, and the thin tube 14 are made with the same quality and heat conductivity and the thermal expansion coefficients thereof are substantially equal. A lower melting-point metal holder 74 is fixed to an outer side face of the thick tube 15. The low melting-point metal holder 74 consists of an insulating material such as ceramic or a super-engineered plastic and a low melting-point metal 75 such as u alloy is insulatively housed in a groove formed on a top face thereof.
A first voice coil motor (VCM) is fitted to the top of the case 1.
This first voice coil motor comprises a magnet 2 having a shaft 3, a needle 4a surrounded by a wound on coil 5, a needle component 4b fixed to the needle 4a, a membrane 6a, and a fixing component 6b fixing an outer circumference of the membrane 6a. A spindle 8 extending in a z direction is fixed to the needle component 4b. A detector 9 for detecting a displacement of a tip 10 is installed in a bottom side end of this spindle 8.
The spindle 8 is supported elastically by first and a second springs 11 and 12 held by the inner tube 13. A heating coil 16 is wound around at a position outside the thick tube 15 and opposite to the viscous material 17. The heating coil 16 is electrified for softening the viscous material 17 in coarse adjustment of the tip 10 in the z direction.
A second voice coil motor, which comprises a magnet 21 having a shaft 22, a needle 23a surrounded by a wound on coil 24, a needle component 23b fixed to the needle 23a, a membrane 25, and a fixing component 25a fixing the outer circumference of the membrane 25, is mounted on a side of the case 1.
A thin annular plate spring 23c is fitted to a lateral side of the case 1 for preventing the needle 23a from making contact with the shaft 22 or the magnet 21, when the thick tube of the scanning tube 20 tilts in an XY direction. At the thin annular plate spring 23c, the outer circumference thereof is pushed by the case 1 and the membrane fixing component 25a and an inner circumference thereof is pushed by the needle component 23b and an annular spring component 23d. A spindle 27 extending in an x direction is fitted to the needle component 23b and the annular spring component 23d. An open end of the spindle 27 is fixed to a projecting portion 15a of the thick tube 15.
A third voice coil motor (not shown) is installed in a direction differing by 90xc2x0 from the second voice coil motor. The third voice coil motor is constituted as being identical or equal to the second voice coil motor. A y direction (a direction at right angles to the paper) spindle connects a movable component fixed to the needle of the third voice coil motor to the thick tube 15. Driving the second and third voice coil motors allows the tip 10 to scan in the xy direction. A sample table (not shown) is mounted at a position opposite the tip 10 and a sample is mounted on the sample table.
An outer tube 71, of which one end is fixed to the case 1, extends to the outside of the thin tube 14 in the direction coaxial with the thin tube 14 and so as to project to the sample chamber. At the outer circumference of a front end of the outer tube 71, a heat conductive cylinder 73 is installed through the insulative member 72 formed from ceramic material. A heating coil 76 is wound around the outer circumference of the heat conductive cylinder 73. The bottom end of the heat conductive cylinder 73 is embedded in the low melting-point metal 75 of the low melting-point metal holder 74.
According to such a structure, controlling electrification of the heating coil 76 for melting or solidifying the low melting-point metal 75 allows switching spring rigidity of the scanning tube 20 to any one of spring rigidity of the thin tube 14 only or spring rigidity created by adding the thin tube 14 to the outer tube 71. As a result, even if the driving current supplied to the voice coil motors is equal, a movable range of the scanning tube 20 in the XY direction can be made to be different to express the zooming function.
When measuring the sample, first, the heating coil 16 of the thick tube is electrified to raise the temperature of the viscous material 17 so as to finally decrease the viscosity of the viscous material 17. Next, the voice coil motor is electrified in a z direction to carry out coarse adjustment of the spindle 8 in the z direction. When the tip 10 makes contact with the sample surface and then an extent of bending reaches a predetermined value, electrification of the voice coil motor is suppressed and moving down of the tip 10 is stopped. At this time, coarse adjustment is completed.
Subsequently, electrification of the heating coil 16 is suppressed to drop the temperature of the viscous material 17 to a preheated temperature. As a result, viscosity of the viscous material 17 increases resulting in the thick tube 15 with the inner tube 13 becoming substantially integral due to the viscosity of the viscous material 17 and the sample therefore becomes measurable.
In the probe scanning device according to the structure as described above, a surface shape of the sample can be accurately measured preferably by lowering a scanning speed of the tip 10 in the xy direction. A resonance frequency of a z axis is a function of a resultant force of a first 11 and a second 12 spring and a mass of the movable portion on the z axis, and thus, if frequency components, when a change of the z axis is subjected to frequency resolution making the scanning speed of the x axis and the y axis to a time axis, contains the resonance frequency of the z axis, increased amplitude is observed in this component. Such resonance can be prevented by lowering the scanning speed in the xy direction.
However, when the scanning speed is decreased, time for measurement necessarily increases.
The viscous material 17 has a small viscosity at preheating temperatures and the inner tube 13 moves down or up slightly against the thick tube 15. Therefore, when measurement time becomes longer, a distance of the inner tube 13 which is moved down or up increases which causes data related to the z direction to contain an error corresponding to the distance made by moving down or up.
When electrification of the heating coil 16 during measurement is limited, the temperature of individual parts containing the thick tube 15 and the inner tube 13 decreases gradually causing thermal shrinkage and data relating to the z direction therefore contains an error corresponding to thermal shrinkage.
The advantage of the present invention is to provide a probe scanning device capable of measurement of high precision and low noise even when measuring at slow scanning speeds.
The present invention is characterized by a probe scanning device having a thick tube extended in a z direction and an end thereof supported by a case, an inner tube passing through the inside of the thick tube, a tip mounted on the front end of the inner tube, a viscous material filled in a space between the thick tube and the inner tube, first heating means for heating the thick tube, scanning means for reciprocally moving the thick tube in an xy direction, a voice coil motor for driving the inner tube towards the thick tube in the z direction, first temperature-controlling means for decreasing viscosity of the viscous material by supplying a driving current to the first heating means, and driving means having a coarse adjustment mode for coarsely moving the tip to a surface of a sample and a measurement mode for fine movement of the tip in the z direction to maintain a given relationship between relative positions of the tip and the sample surface after coarse movement, wherein fixing means for selectively fixing the thick tube and the inner tube are also provided.
(1) The probe scanning device has a fixing means for selectively fixing the thick tube and the inner tube.
(2) The probe scanning device is characterized in that the fixing means comprises: a low melting-point metal holder fixed to the inner tube and insulatively housing a low melting-point metal, a heat conductive member fixed to the thick tube through an insulant and with an end thereof being positioned so as to be embedded in the low melting-point metal, second heating means for heating the heat conductive member, second temperature-controlling means for controlling the supply of driving current to the second heating means in order to allow a temperature of the heat conductive member to rise to a first temperature, at which the low melting-point metal softens during coarse adjustment, and drop to a second temperature, at which the low melting-point metal hardens during measurement.
(3) There is also provided means for detecting an offset current contained in a driving current of the voice coil motor, wherein the first temperature-controlling means controls a driving current to be supplied to the first heating means to raise the temperature of the thick tube to a temperature, at which viscosity of the viscous material drops during coarse adjustment, and allows the temperature, at which the offset current is reduced in the measurement, to be reached.
(4) The probe scanning device is characterized in that each temperature-controlling means comprises holding means for holding a driving signal, which is supplied to each heating means, during measurement.
According to the characteristic (1) as described above, the thick tube and the inner tube are firmly fixed by the solidification of the low melting-point metal and a positioning shift with respect to time can therefore be prevented.
According to the characteristic (2) as described above, the temperature of the heat conductive cylinder is lowered to a temperature at which the low melting-point metal is solidified, and heat shrinkage of the heat conductive cylinder in the z direction can be cancelled by thermal expansion of the thick tube and the inner tube.
According to the characteristic (3) as described above, the temperature drift caused by a temperature change during measurement can be eliminated not by supplying the offset current to the voice coil motor, but rather by thermal expansion or heat shrinkage of the thick tube and the inner tube.
According to the characteristic (4) as described above, an output signal from a first and second temperature-controlling unit are held during measurement and hence, regardless of the change of an ambient temperature and temperature drift in a controlling system, an image with less noise can be obtained.